Tijuana River Pilot Channel & Smuggler’s Gulch Channel Attachment 1 - Individual Maintenance Plan Introduction The City of San Diego (City) Master Storm Water System Maintenance Program (Master Maintenance Program or MMP) is currently planning for implementation of channel maintenance activities in the Smuggler’s Gulch (SG) and the Tijuana River Pilot (Pilot) Channels. This Individual Maintenance Plan (IMP) identifies the scope of work, maintenance methodology and procedures, equipment, and duration for maintenance activities planned in the two channels. The IMP also includes a list of Best Management Practices (BMPs), maintenance protocols and mitigation measures derived from applicable permits and regulations that will be implemented with the intent to avoid, minimize, and/or mitigate potential environmental effects to sensitive resources, such as water quality, biological and historical resources. Scope of Work The proposed maintenance of the SG and Pilot Channels includes the mechanized removal of sediment, vegetation and trash and debris from the channels using heavy equipment. In addition, pre-maintenance work in the eastern portion of the Pilot Channel includes the pumping of accumulated stagnant ponded water from winter and spring rains downstream in order to sufficiently dry out the channel and allow for mechanized excavation. If needed, the pumping of ponded water may be continued during the maintenance activities to transport ponded water to the western end of the Pilot Channel and sufficiently dry the work area. The periodic maintenance of both channels is needed to restore the channels’ flood conveyance capacity to their original design condition and to protect the Tijuana River National Estuarine Research Reserve from impacts due to downstream transport of accumulated sediment and trash and debris from the project area. The project incorporates removal of approximately 10,000–30,000 cubic yards of material, occupying a total of 4.31 acres. The SG Channel and Pilot Channel are depicted in the MMP Maps 138 and 139, and Maps 138a and 138c, respectively, and are shown on Sheet 1 of the Construction Plans. Impact Area The SG Channel and Pilot Channel are located in the Tijuana River Valley (Valley), within the jurisdiction of the City of San Diego (City) (Figure 1). The Tijuana River watershed covers an area of approximately 1,725 square miles, of which 73 percent is located in Mexico and 27 percent in the United States. The main Tijuana River flows in a northwesterly direction from the international border into the Valley and City Page 1 Tijuana River Pilot Channel & Smuggler’s Gulch Channel Attachment 1 - Individual Maintenance Plan jurisdiction. Approximately 21.9 square miles of the watershed (~1% of the total watershed area) is within City jurisdiction. The Tijuana River National Estuarine Research Reserve (TRNERR) and a portion of the City of Imperial Beach are generally west of the project area located adjacent to the Tijuana River’s discharge to the Pacific Ocean. The Otay-Nestor community and the United States Naval Outlying Landing Field Imperial Beach are located north of the project area; and the community of San Ysidro is located to the east. The Pilot Channel is included on MMP Maps 138a through 138c and the SG Channel is included on MMP Maps 138 and 139 (City of San Diego 2011a). The Pilot and SG Channels are generally located in the Valley roughly bordered by Hollister Street to the east and Monument Road to the south. The Tijuana River low flow channel splits into what are commonly referred to as the Tijuana River’s Northern and Southern Channels approximately 800 feet east of Hollister Street. The Pilot Channel follows the Southern Channel. The Valley, including the project area, is within the Federal Emergency Management Agency’s (FEMA) Special Flood Hazard Areas Subject to Inundation by the 1-percent Annual Chance Flood (100-year floodplain). The project areas are zoned OF-1-1 (Open Space-Floodplain) and AR-1-1 (Agricultural/Residential); and are designated for Open Space and Agricultural land uses in the Tijuana River Valley Land Use Plan. In addition, the project area is within the boundaries of the County of San Diego’s 2.7 square mile Tijuana River Valley Regional Park (Regional Park). The project area is also within the City’s Multiple Species Conservation Program’s Multi-Habitat Planning Area (MHPA). The project consists of maintenance and dredging of the Pilot and SG channels to remove anthropogenic-derived sediment and trash that accumulates as a result of development and other practices in the upstream watershed. Recent maintenance efforts within the Pilot Channel and SG Channel include maintenance in fall 2009 through winter 2010, fall 2010, and fall 2013 through winter 2014. The removal of sediment and trash is conducted to maintain flow conveyance capacities and reduce the risk of flooding to public and private infrastructure in the Valley. Pilot Channel The Pilot Channel was originally excavated in 1993 within the Southern Channel. It is has been irregularly maintained since that time as an earthen trapezoidal channel that is approximately 5 feet deep, with a 23-foot top width, and a 15-foot streambed width. According to the MMP, the Pilot Channel was constructed to divert wet-weather flows from 2- to 5-year storm events into the Southern Channel (City of San Diego 2011b). The Page 2 Tijuana River Pilot Channel & Smuggler’s Gulch Channel Attachment 1 - Individual Maintenance Plan Pilot Channel stretches from 100 feet east to 5,300 feet west of Hollister Street for a total length of 5,400 feet and it flows roughly in an east-west direction. Previous maintenance under the MMP has not included channel clearing in the project area east of the Hollister Street bridge due to the presence of stagnant ponded water. As the ponded water is removed, City maintenance staff will assess the amount of accumulated sediment, trash and debris present in the Pilot Channel east of the Hollister Street bridge within the project area. Based on the assessment, channel clearing to restore the approximate 5 feet deep, with a 23-foot top width, and a 15-foot streambed width of the Pilot Channel in this area may be conducted. At the conclusion of maintenance activities, trail access from the area north of the Pilot Channel adjacent to the confluence of the Pilot Channel and Smuggler’s Gulch channel to the area south of the Pilot Channel, west of Smuggler’s Gulch will be repaired. The repair will include grading of an approximate 8 foot wide section within the 23-foot top width of the Pilot Channel using native soils to re-establish the trail connection using a maximum 3:1 slope with a 4:1 slope preferred. Pre-maintenance pumping to dry the eastern portion of the Pilot Channel will likely occur in stages. The pumping process will begin with the placement of a suction hose within the Pilot Channel near Hollister Street Bridge, placing a pump adjacent to the channel, and the placing of temporary hoses along the channel bank to a discharge location, likely near the confluence of the Pilot Channel and SG Channel. The second stage would involve a similar set up of equipment placed further downstream to pump water from the confluence to the downstream (western) end of the Pilot Channel. Additional pumping may be required if rains occur during the project and result in ponded water pools within the work area. SG Channel The SG Channel is an existing historical agricultural channel with manufactured berms. The contributing sub-watershed area is approximately 6.7 square miles, primarily located south of the international border within Canon de los Mataderos. The SG Channel, as originally constructed, is an earthen channel approximately 20 feet wide and 15 feet deep. The SG Channel is tributary to the South Channel and flows in a northerly direction, from the international border past Monument Road until it confluences with the Pilot Channel. The portion of the SG Channel maintained by the City extends for a distance of approximately 3,040 feet. Three equipment turnarounds (extending beyond the 23-foot wide Pilot Channel maintenance corridor an additional 25 feet in width for a length of approximately 30 feet Page 3 Tijuana River Pilot Channel & Smuggler’s Gulch Channel Attachment 1 - Individual Maintenance Plan along the channel) are sited immediately adjacent to the Pilot Channel, and are required for maintenance activities. Two of the turnarounds are located west of the Pilot Channel confluence with the SG Channel and were constructed and utilized during the 2009 maintenance activities. The third turnaround is located east of this confluence and will be constructed as part of this project. All three turnarounds are necessary for equipment movements within the confined channel work area. It is expected that the turnarounds would remain at the same locations for future maintenance needs for the project. Staging and Stockpiling Areas Maintenance operations will remove a large volume of sediment and require the use of temporary stockpile sites to store and process excavated material prior to transport. Two temporary staging areas, Staging Areas B and D, will be used to store equipment and materials during maintenance operations, and will also be used as stockpile sites (refer to Figure 1). Staging Area B is east of and adjacent to the SG Channel. There is a permanent earthen berm between this area and the SG Channel, protecting it from potential flooding. Permanent gated access to the staging area is from Monument Road. This staging area was initially used in 2001 and has been used during each maintenance event since that time, by both the City and County of San Diego. No excavation or grading would be necessary in this area other than minor trenching and clearing to install temporary silt fencing and BMPs.